Thrombopoietin (TPO), also called megakaryocyte growth and development factor (MGDF), thrombocytopoiesis stimulating factor (TSF), c-myeloproliferative leukemia ligand (c-Mpl), mpl ligand, or megapoietin, is a glycoprotein that has been reported to regulate the production of platelets. See Wendling, F., et. al., Biotherapy 10(4): 269-77 (1998); Kuter D. J. et al., The Oncologist, 1: 98-106 (1996); Metcalf, Nature 369: 519-520 (1994).
Under certain circumstances, the activity of TPO results from the binding of TPO with the TPO receptor (also called Mpl). The TPO receptor has been cloned and its amino acid sequence has been described. See Vigon et al., Proc. Nat. Acad. Sci., 89: 5640-5644 (1992).
TPO is a 332-amino acid glycosylated polypeptide that plays a key role in the regulation of megakaryocytopoiesis, and in the process in which platelets are produced by bone marrow megakaryocytes. See Kuter et al., Proc. Nat. Acad. Sci. USA 91: 11104-11108 (1994); Barley et al., Cell 77:1117-1124 (1994); Kaushansky et al., Nature 369:568-571 (1994); Wendling et al., Nature 369: 571-574 (1994); and Sauvage et al., Nature 369: 533-538 (1994). TPO is produced in the liver but functions mainly in the bone marrow, where it stimulates the differentiation of stem cells into megakaryocyte progenitors, and stimulates megakaryocyte proliferation, polyploidization and, ultimately, enters the platelet circulation in the body. TPO is also a primary regulator in situations involving thrombocytopenia and in a number of studies that include increasing platelet counts, platelet size and isotope incorporation into platelets of recipient animals. See, Metcalf Nature 369: 519-520 (1994). Specifically, TPO is considered to affect megakaryocytopoiesis by several ways: (1) it causes increase in size and number of megakaryocyte; (2) it increases DNA contents, the forms of polyploidy, and the number of megakaryocytes; (3) it increases megakaryocyte endomitosis; (4) it increases the number of mature megakaryocytes; (5) it increases the percentage of precursor cells, the number of small acetylcholinesterase positive cells, the number of bone marrow cells.
Platelets are necessary for blood clotting. When platelet counts are very low, a patient is at risk of death from catastrophic hemorrhage. Thus, TPO has been used for both the diagnosis and the treatment of various hematological disorders, for example, diseases primarily caused by platelet defects. Likewise, TPO may be useful for the treatment of thrombocytopenic conditions, especially those derived from chemotherapy, radiation therapy, or bone marrow transplantation for the treatment of cancer or lymphoma.
The slow recovery of platelet levels in patients suffering from thrombocytopenia is a serious problem, it is desirable to provide a compound for the treatment of thrombocytopenia by acting as a TPO mimetic. These peptides were designed to bind and activate the TPO receptor (TPO-R) but have no sequence homology to the natural TPO. In recent years, a number of active small-molecule TPO mimetics have been reported, including cyclic polyamine derivatives (WO00/28987), thiazol-2-yl-benzamides (WO01/07423, WO01/53267), azo-aryl derivatives (WO00/35446, WO01/17349), 2-aryl-naphthimidazoles (WO01/39773, WO01/53267), and semicarbazone derivatives (WO01/34585). In cell-based systems, all of these molecules can activate signal transduction pathways that are dependent on the presence of the TPO receptor on the cell membrane. Certain types of compounds can directly act on the TPO receptor itself. Some of the most preferred compounds of this series were found to stimulate the proliferation and differentiation of TPO-responsive human cell lines and TPO in human bone marrow cultures that has a concentration below 100 nM.
Several patents assigned to GlaxoSmithKline described a thrombopoietin analog, eltrombopag (WO-2003098992/WO-01089457), with good activity.
The present disclosure provides a series of pharmaceutical acceptable salts of bicyclo-substituted pyrazolon-azo derivatives, which are more effective TPO mimetics and TPO receptor agonists.
The international application no. PCT/CN2009/000001 submitted by the applicant of the present invention on 4 Jan. 2009 described a novel bicyclo-substituted pyrazolon-azo derivatives and their use as thrombopoietin (TPO) mimetics and agonists of the thrombopoietin receptor. Six examples (Example 1, Example 9, Example 15, Example 28, Example 43 and Example 52) described in the international application provided the compounds respectively as follows: 2′-hydroxy-3′-[N′-(1-indan-5-yl-3-methyl-5-oxo-1,5-dihydro-pyrazol-4-ylidene)-hydrazino]-biphenyl-3-carboxylic acid, 5-{2-hydroxy-3-[N′-(1-indan-5-yl-3-methyl-5-oxo-1,5-dihydro-pyrazol-4-ylidene)-hydrazino]-phenyl}-furan-2-carboxylic acid, 5-(2-hydroxy-3-{N′-[3-methyl-5-oxo-1-(5,6,7,8-tetrahydro-naphthalen-2-yl)-1,5-dihydro-pyrazol-4-ylidene]-hydrazino}-phenyl)-furan-2-carboxylic acid, 4-(2-hydroxy-3-[N′-(3-methyl-5-oxo-1-(5,6,7,8-tetrahydro-naphthalen-2-yl)-1,5-dihydro-pyrazol-4-ylidene)-hydrazino]biphenyl-furan-2-carboxylic acid, 5-(3-{N′-[1-(3,3-dimethyl-indan-5-yl)-3-methyl-5-oxo-1,5-dihydro-pyrazol-4-ylidene]-hydrazino}2-hydroxy-phenyl)-furan-2-carboxylic acid, 4-{2-hydroxy-3-[N′-(1-indan-5-yl-3-methyl-5-oxo-1,5-dihydro-pyrazol-4-ylidene)-hydrazino]-phenyl}-thiophene-2-carboxylic acid, and the esters thereof. These compounds were tested to show good activity as TPO receptor agonists. Therefore this international application was whole incorporated here by reference. However, the international application no. PCT/CN2009/000001 didn't describe the pharmaceutical acceptable salts of the compounds.
The inventor of the disclosure discovered that the free acid form of bicyclo-substituted pyrazolon-azo derivatives were poorly soluble in conventional solvents, and thus disadvantageous to be prepared into a medicinal dosage form, limiting their in vivo bioavailability. It is necessary to develop new forms of bicyclo-substituted pyrazolon-azo derivatives to improve their solubility and pharmacokinetic absorption, which can be used in conventional preparation of dosage forms.